1. Field of the Invention
The present invention relates to a voltage regulator including a protection circuit.
The present application claims priority based on Japanese Patent Application No. 2016-007340 filed in Japan on Jan. 18, 2016, the disclosures of which are incorporated herein by reference in their entirety.
2. Description of the Related Art
In general, electronic devices such as cellular phones are configured to operate with rechargeable batteries. A voltage regulator is provided to the battery such that an output voltage to the electronic device does not fluctuate and the electronic device stably operates, even when a charged state of the battery fluctuates. Further, the voltage regulator, which is configured to prevent the output voltage to the electronic device from fluctuating such that the electronic device stably operates even when a load of the electronic device sharply fluctuates, is provided with a control circuit for achieving a more stable output voltage of the voltage regulator in some cases.
FIG. 3 is a circuit diagram of a related-art voltage regulator 30. The voltage regulator 30 includes an output transistor 31 configured to output an output voltage VOUT, voltage-dividing resistors 32 for dividing the output voltage VOUT such that a divided voltage VFB is output, an error amplifier circuit 35 configured to operate to match the divided voltage VFB with a reference voltage VREF, and control the output transistor 31 such that the output voltage VOUT is constant, a protection circuit 33 configured to protect the voltage regulator 30, and a control circuit 34 configured to detect fluctuation in output voltage VOUT to operate to stabilize the output voltage VOUT.
The protection circuit 33 is configured to detect failure including, for example, a case in which an excessive current flows through the output transistor 31, and output a signal at a power supply voltage level to perform control for turning off the output transistor 31.
The control circuit 34 is configured to detect decrease in output voltage VOUT to perform control for turning off the output transistor 31.
Here, the control circuit 34 is configured to stop its operation when receiving the signal at the power supply voltage level that indicates that the protection circuit 33 has started to operate. Thus, when the output voltage VOUT is decreased through control by the protection circuit 33, the output voltage VOUT is not increased through operation of the control circuit 34. As a result, safety of the voltage regulator is increased (for example, see Japanese Patent Application Laid-open No. 2008-204018).
However, the protection circuit 33 only has an analog signal having an intermediate potential, as means for detecting failure, such as a voltage. Thus, for the protection circuit 33, a circuit configured to convert an output signal being an analog signal into a digital signal is required.